1. Field of the Invention
The present invention relates to ammunition, and more particularly to low vulnerability gun propellants and novel polymers for use therein.
2. Description of the Prior Art
A continuing objective in the design of gun propellants is to provide a gun propellant which is energetic when deliberately ignited, but which exhibits high resistance to accidental ignition from heat, flame, impact, friction, and chemical action. Propellants possessing such resistance to accidental ignition are known as "low vulnerability" (often abbreviated as LOVA) gun propellants.
LOVA gun propellants are well-known in the prior art. One approach for producing low vulnerability gun propellants has been the use of polyurethane binders. For example, U.S. Pat. No. 4,091,729, to Bell et al, describes a main propellant charge which includes 25% by weight of 1,3,5,7-tetramethylenetetranitramine (HMX) or 1,3,5-trimethylenetrinitramine (RDX), in combination with 75% by weight of polyurethane binder. The polyurethane binder comprises 11.867% by weight of a hydroxyl-terminated block copolymer of propylene oxide and ethylene oxide, 3.167% by weight of trimethylol propane, 9.967% by weight of lysine diisocyanate methyl ester, and 0.025% by weight of titanyl acetyl acetonate. After mixing, the propellant is extruded and placed in a curing oven in the form of small diameter tubes.
However, the propellants of the prior art suffer from the disadvantages that they are not readily extruded with multiple perforations, and their mass impetus is only about 336,000 ft-lbf/lbm. While the mass impetus of such a prior art propellant is acceptable, a higher mass impetus is desirable. In addition, when extruded, a polyurethane such as that described in U.S. Pat. No. 4,091,729 can slump prior to cooling resulting in the partial closure of any perforations. "Slumping" is the tendency of an extruded material to flatten out rather than retaining its shape when placed on a flat surface while cooling and solidifying. Thus if the propellant as extruded is round in cross section, the material will tend to flatten out against the supporting surface.
Accordingly, a need exists for a polymer useful in making a low vulnerability gun propellant which exhibits a desirably high mass impetus value and lends itself to the extrusion of multi-perforated propellant grains which will retain their extruded shape without slumping.